This invention relates in general to certain new and useful improvements in data transmission systems, and, more particularly, to simplified data transmission systems which modulate and demodulate pulse trains of binary data and clock pulses.
In recent years, modems (modulators and demodulators) have widespread employment in communication systems where communication is desired between two or more remote pieces of digital equipment. It is recognized that this communication is achieved by means of modems which transmit the data over a transmission link and, at another remote source, receive the data from the transmission link. In many cases, this transmission link may adopt the form of a voice grade communication link, such as a conventional telephone communication link. Notwithstanding, the information communication link may also adopt other forms of communication connections.
The modem is specifically designed to encode the data, which normally exists in a digital format, into an analog form suitable for transmission, and thereafter to accomplish decoding for reconversion of the data into the digital format. These devices usually employ a transmitter which generates a carrier signal and modulates the carrier signal with data to be transmitted. In like manner, a receiver may also be relocated at the remote source for demodulating the carrier and removing the data therefrom.
The presently available modems operate on either asynchronous basis, that is transmission of data without clock information, or, otherwise, on a synchronous basis, where clock information is transmitted on the data track along with the digital data.
One of the primary problems of the presently available synchronous modems, particularly when used on short-distance transmission lines, resides in the fact that these modems are fairly complex in their design. Moreover, these devices are relatively expensive in order to achieve the necessary compression of required bandwidth from the transmission link. In many cases, these modems also require the DC voltage connection from the transmitter to the receiver. In most cases, the modems operate on the basis of transmitting the data information by means of a carrier signal which is generated by a carrier oscillator. Nevertheless, these commercially available modems, which are highly sophisticated, are rather expensive and hence commercially and economically unfeasible for use in a short distance communication.
The present invention obviates these and other problems in the provision of a modem which serves as a substitute for the conventional synchronous modem and eliminates the necessity of a carrier signal. In the modem of the present invention, the data signals are combined with clock pulses for transmission over the voice grade communication links and permits generation of the encoded signals from the combination of the clock pulses and data. The present invention also includes a receiver for decoding the received wave form, in analog format, and permits separation of the data from clock pulses.
It is, therefore, the primary object of the present invention to provide a synchronous modem which is an effective replacement for conventional synchronous modems and which is able to be used on short distance voice grade transmission links.
It is another object of the present invention to provide a modem of the type stated which is relatively simple in its design, but which nevertheless achieves a reasonable compression of required bandwidth from the transmission link and requires no direct DC connection between the transmitter and the receiver in the modem.
It is a further object of the present invention to provide a modem of the type stated which incorporated all of the advantages of a simplified transmitter for purposes of generating a transmitted waveform without the attendant requirement of a carrier signal produced by a carrier oscillator.
It is an object of the present invention to provide a modem of the type stated which is capable of transmitting the data information by combining the data waveform with clock pulses of the type normally present in digital type equipment.
It is an additional object of the present invention to provide a modem of the type stated which may be constructed at a relatively low cost, but which has a high degree of efficiency and may be simply constructed with present-day integrated circuitry technology.
It is another salient object of the present invention to provide a method of transmitting data on short distance voice communication links by combining the data with clock pulses for purposes of transmission and thereafter separating the clock pulses from the data for recovery of the data.
With the above and other objects in view, my invention resides in the novel features of form, construction, arrangement, and combination of parts presently described and pointed out in the claims.